The use of blowout preventers (BOPs) in oil and gas fields is well known. A blowout preventer generally includes a housing with a bore extending through the housing. Opposed chambers extend laterally from the bore in the housing and communicate with the bore. Rams are positioned in the opposed chambers and the rams are connected to rods that are supported for moving the rams inwardly into the bore to close off the bore, thereby defining a zone above the rams and a zone below the rams. The force for moving the rams into the bore is commonly provided by respective hydraulically operated pistons coupled to the rods, with each piston enclosed within its respective operating cylinder. The rods also serve to retract outwardly from the bore to open the bore. In many BOPs, tail rods extend from the pistons outwardly of the operating cylinder of the pistons.
Various types of rams may be employed such as those which engage circumferentially around a tubular member extending through the BOP, such as for example coiled tubing, drill pipe, production pipe, or the like. The term “tubing” used herein refers to any of these types of tubular member. The BOP ram may provide for sealing engagement with the tubular member, while other types of BOP are provided with cutting surfaces for shearing the tubular member which extends through the bore of the blowout preventer.
Among other uses, BOPs are commonly used in oil and gas exploration and production systems as a means of holding the tubular member and isolating the well bore pressure during a variety of conditions, including emergencies. The configuration of the BOP rams and side port facility allow well-control operations to be conducted under a variety of conditions.
For example, blowout preventers are commonly used to seal a wellbore. In drilling operations, the pressure in the wellbore is adjusted to at least balance formation pressure by increasing drilling mud density in the wellbore or increasing pump pressure at the surface of the well. At times, a drill bit may penetrate a down hole layer having a pressure higher than the pressure maintained in the wellbore. In this event, it may be necessary to deploy the blowout preventer to prevent damage to equipment or harm to personnel above the well bore.
When the blowout preventer is deployed, one region of the blowout preventer that presents a possible point of leakage is the joint between the blowout preventer body and the bonnet. Commonly, an elastomeric O-ring seal is positioned in a depression between the body and the bonnet and crushed as the bonnet is bolted to the body. The friction force between the O-ring seal and the mating surfaces on the body and bonnet provide the seal against fluid leakage under pressure.
This type of seal works well for sealing normally encountered pressure at a well head. Unfortunately, for higher pressure applications, this type of seal has been known to leak. Also, care must be exercised in aligning the seal so that an even force is applied around the entire perimeter of the seal. Otherwise, a weak spot will be installed with the installation of the seal.
Thus, there remains a need for a body to bonnet seal that is capable of withstanding higher pressures. Such a sealing device should be self aligning and should be impervious to the harsh environment in which the seal finds application, such as for example down hole. The seal described herein solves these and other problems in the art.